Production of synthetic resinous materials



J1me 1953 c. G. EVANS' ET AL PRODUCTION OF- SYNTHETIC RESINOUS MATERIALS Filed June 13, 1949 a G. Evbns 4 f RAM Elk/o lngenz ns Attorneys Patented June 2, 1953 PRODUCTION OF SYNTHETIC RESINOUS MATERIALS Cyril G. Evans, Farnborough, and Peter H. H.

Bishop, Gosport, England, assignors to Minister of Supply in His Majestys Government,

London, England Application June 13, 1949, Serial No. 98,854 In Great Britain July 2, 1948 4 Claims. 1

This invention relates to the production of synthetic resinous materials and more particularly to their reinforcement with asbestos fibres.

It is known that the strength and stiffness of materials with fibrous reinforcement are affected by the mutual relationship of the individual fibres and by their general orientation in relation to the direction of applied stresses; it is known, furthermore, that the maximum compressive and tensile strengths can only be obtained when the fibres are parallel to each other and to the direction of stress.

In the usual commercial methods of breaking down asbestos rock into fibre, the rock is crushed in such a way that there results a random mass of relatively short fibres which is subsequently treated, either by carding and spinning or by felting. Any attempt to employ the usual commercial products in the production of materials with reinforcing fibres in a desired parallel relationship involves further intermediate steps. When asbestos rock is crushed, the crystalline structure splits along natural planes of cleavage to provide bundles of substantially parallel fibres; thus, any intermediate steps which results in or are designed to correct any other (temporary) relationship of the fibres must be considered as wasteful. Furthermore, the usual intermediate commercial treatments, such as carding, result in splitting of the asbestos to a greater degree than results from the initial crushing of the rock.

According to the present invention, the substantially parallel relationship of asbestos fibres resulting from crushing of asbestos rock is preserved by impregnation of a mass'of fibres with the material which they are to reinforce: when the impregnate sets, a material results in which the desired parallel relationship of the fibres has been obtained without the intervention of wasteful operations.

Comparative tests have shown that asbestosreinforced material can be produced in accordance with the invention to exhibit greater comcomprising commercially extracted fibres, the very small fibres call for a high percentage of resin (actually greater than that of the strengthgiving asbestos) to bond them together; further, the wetting of the individual fibres is possibly incomplete. In the case of the material produced in accordance with the invention, the rock splits along the weakest planes. of cleavage, leaving the stronger natural bonds, the material involved in which would be considered impurity in asbestos extracted for other commercial purposes; the comparatively large fibres can be fairlyeasily wetted and their bonding together requires a relatively small weight of resin, actually less than that of the asbestos. The relative increase in compressive strength results from the greater stability in compression of the individual fibres due to their greater cross section and this increased stability enables the fibres to bridge larger defects in the bonding without buckling. The comparatively low value of the ratio tensile strength/compressive strength may be due to the low value of, the ratio surface area/ cross sectional area which entails a relatively larger shear at the surface of the fibre to develop the full tensile strength of the fibre. Thus, the ratio compressive strength/tensile strength can be regulated as desired, within limits, by appropriate control of the degree of crushing.

The preferred manner of carrying out the invention is illustrated by the accompanying diagrammatic drawing wherein asbestos rock'is indicated at H in process of being fed to crushing rolls l2 and I3 (which, in practice, may bethe first pair of a series of crushing rolls) the rock is fed so that the natural planes of cleavage are orientated substantially normally to the axes of the rolls. Upon leaving the rolls, or the last pair of rolls, the resultant bundles of fibres are fed between a pair of superimposed travelling belts M and I5 of copper gauze guided by pulleys which are not illustrated in the drawing. The belts carry the fibrous mass through a bath E5 of the material with which the mass of fibres is to be impregnated, for Xample partially condensed phenoliormaldehyde resin, which is indicated at ll. Upon leaving the bath, the belts pass between rollers l 3 and 19, which squeeze excess liquid from the fibrous mass. Beyond the squeezing rollers, the upper belt M is led away and a web 26 of thin paper is brought into contact (by a pulley, not shown) with the impregnated mass still carried by the lower belt; although the resin will not adhere to the copper gauze, it will adhere to the paper to form a paper-backed sheet of resinous material reinforced with substantially parallel asbestos fibres. The belt and web pass through a drying device 21, whereby the paperbacked sheet 22 is rendered tack free for the facilitation of handling before being led away, as indicated by the arrow, for storage either immediately or after passage through a calendering machine.

In cases where the presence of a paper backing is objectionable, it may be dispensed with, the impregnated mass being formed into sheets simply by drying. Unbacked sheets are probably preferable in most cases, but they are, of course, more susceptible to damage in handling.

Sheets formed as just described may be stacked and the resin cured to form a stiff material of the desired thickness. The individual paperbacked or unbacked sheets may be stacked so that all the fibres are substantially mutually parallel or the fibres in individual layers may bear any angular relation to those of other layers as necessary to obtain the strength and stiffness characteristics required of the finished product.

Crocidolite and the coarser grades of chrysotile type asbestos rocks are suitable raw materials and it is considered though not yet proven, that picrolite should be a highly suitable starting material; not only should fibre from this source be cheap, being a'by-product of the extraction of the chrysotile type asbestos, but the fibres naturally exhibit a desirable coarseness.

If curing at relatively low temperature, say 100 0., is desired, the fibrous masses which are to be stacked in adjacent layers may be impregnated with different constituents of composite resins as described in the specification accompanying co-pending United States application Serial No. 84,768, filed March 31, 1949, now abandoned.

We claim:

1. A method of producing synthetic resinous material reinforced with substantially parallel asbestos fibres comprising only the steps of feeding asbestos rock to a series of crushing rolls, the natural planes of cleavage of said asbestos rock being oriented substantially norm-ally to the axes of said crushing rolls, impregnating the mass of fibres resulting from said crushing with synthetic resinous material to retain the positional relation of said fibres, the relative positions of said fibres being kept substantially the same between said crushing step and said impregnating step, and drying said impregnated mass.

2. The method of producing synthetic resinous material in an uninterrupted series of successive operations, the steps comprising: crushing asbestos rock, said crushing step producing a mass of substantially mutually parallel fibres, immersing said mass of fibres in liquid resinous material, said fibres being retained in their original relative substantially parallel positions during the immersion, squeezing excess liquid from said fibres to produce a mass of substantially mutually parallel asbestos fibres impregnated with resinous material, and drying said impregnated fibres.

3. A method of producing synthetic resinous material reinforced with asbestos fibres in substantially parallel mutual relationship, in which the substantially parallel mutual relationship of the fibres of asbestos rock is substantially maintained and which comprises crushing asbestos rock as a first operation, said crushing step producing a mass of substantially mutually parallel fibres; and then impregnating the crushed material with synthetic resinous material as the next following operation, the relative positions of said fibres being kept substantially the same between said crushing and said impregnating operations. 4. A method of producing synthetic resinous material reinforced with substantially parallel asbestos fibres comprising only the steps of feeding asbestos rock to a series of crushing rolls, the natural planes of cleavage of said asbestos rock being oriented substantially normal to the axes of said crushing rolls, crushing said rock, said crushing step producing a mass of substantially mutually parallel fibres, impregnating the mass of fibres resulting from said crushing with synthetic resinous material to retain the positional relation of said fibres, the relative position of said fibres being kept substantially the same between said crushing step and said impregnating step, and drying said impregnated mass.

CYRIL G. EVANS. PETER H. H. BISHOP.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 367,424 Merrill Aug. 2, 1887 1,340,535 Garcin May 18, 1920 1,799,506 Frederick Apr. '7, 1931 1,823,136 Frederick Sept. 15, 1931 1,953,457 Baer Apr. 3, 1934 2,249,275 Hanley July 15, 1941 2,327,991 Betts Aug. 31, 1943 2,459,240 Pharo Jan. 18, 1949 

1. A METHOD OF PRODUCING SYNTHETIC RESINOUS MATERIAL REINFORCED WITH SUBSTANTIALLY PARALLEL ASBESTOS FIBRES COMPRISING ONLY THE STEPS OF FEEDING ASBESTOS ROCK TO A SERIES OF CRUSHING ROLLS, THE NATURAL PLANES OF CLEAVAGE OF SAID ASBESTOS ROCK BEING ORIENTED SUBSTANTIALLY NORMALLY TO THE AXES OF SAID CRUSHING ROLLS, IMPREGNATING THE MASS OF FIBRES RESULTING FROM SAID CRUSHING WITH SYNTHETIC RESINOUS MATERIAL TO RETAIN THE POSITIONAL RELATION OF SAID FIBRES, THE RELATIVE POSITIONS OF SAID FIBRES BEING KEPT SUBSTANTIALLY THE SAME BETWEEN SAID CRUSHING STEP AND SAID IMPREGNATING STEP, AND DRYING SAID IMPREGNATED MASS. 